Molecular statics calculations were used to estimate the energy barriers which corresponded to the general 6-jump cycles in this material. It was found that the [110] 6-jump cycle involved the lowest migration barriers among other possible cycles in the B2 structure, and had the highest probability of occurrence. The attempt frequencies of various jumps were calculated within the quasi-harmonic approximation. A Monte Carlo approach, with a residence-time algorithm, was then used to analyze diffusional correlation effects. The temperature dependence of Ni diffusion, via the 6-jump mechanism was found to obey the Arrhenius law:

D (m2/s) = 3.12 x 10-5 exp[-3.12(eV)/kT]

at 800 to 1500K. These values agreed well with experimental results for 63Ni tracer diffusion in monocrystalline samples of stoichiometric composition. The analysis predicted that the 6-jump cycles could be easily broken if the vacancy encountered certain configurations. The resultant contribution of the 6-jump cycle mechanism to the total Ni diffusivity was estimated to be less than about 30% below 1100K, for a perfect stoichiometric composition. The effectiveness of the 6-jump cycles decreased rapidly with deviations from stoichiometry and/or increases in temperature.

On the Six-Jump Cycle Mechanism of Self-Diffusion in NiAl. S.Divinski, C.Herzig: Intermetallics, 2000, 8[12], 1357-68